The present invention relates to new hydrosoluble zwitterion polymers, and to the preparation and uses thereof.
Owing to their compositions and to their molar masses, hydrosoluble polymers of synthetic or natural origin are commonly used at low concentrations as modifying agents for modifying the properties of aqueous solutions and, by action on suspended particles, as modifying agents for modifying surface properties.
In this respect, the use of polycationic polyelectrolytes of dialkylammonium polyalkylene type is notably known, which provide aqueous solutions and polyanionic hydrosoluble polymers such as sodium sulfonate polynaphthalenes or polyacrylates, which allow dispersion of minerals in water, with a high viscosifying effect.
Their use involves certain limitations linked with the sensitivity and the instability of the solutions, notably in the presence of salts or as a result of a temperature rise and, in some cases, because of their harmful effect on the environment.
The zwitterion hydrosoluble polymers of the present invention prove to be efficient as viscosifying agents for aqueous solutions within a wide salinity and temperature range and as modifying agents for the surfaces of particles in aqueous suspensions, and they are furthermore better accepted on account of a better environmental compatibility.
The applications of this type of zwitterion hydrosoluble polymers are those which are generally used in the petroleum industry as oil well fluids, in the paint industry as pigment compatibilizing additives, in the cosmetics and paper industry and, without restricting the use thereof, as treating agents for clays in the photographic film industry and for drilling muds notably. They are also used as rheology control agents for aqueous suspensions.
On account of their structure, the polymers according to the invention can also have properties of drag reducer additives for the flow of certain fluids, notably on eddy flow. These additive types limit the friction of fluids on the walls.
For the formulation of oil well fluids, drilling fluids and completion or production fluids, potential applications can be mentioned such as, for example, the filtrate reducing effect, the clay swelling inhibiting effect, the cuttings or clays crumbling inhibiting effect. The performance level of the zwitterion hydrosoluble polymer defied in the invention will then have to be selected according to the application and therefore to the desired properties.
The polymers conventionally used in water-base fluids are acrylamide derivatives, generally acrylamide/acrylate copolymers obtained by copolymerization of acrylamide and acrylate or by polyacrylamide hydrolysis.
They are however sensitive to the conditions of use that can be encountered. A high shear gradient, a high bottomhole temperature lead to a decrease in their molar mass and in their viscosifying power. Furthermore, they are sensitive to media with high ionic strengths because of the presence of carboxylate or sulfonate groups which also lead to a loss of their viscosifying power or even to a precipitation of the molecules in media with high divalent ions concentrations.
For applications in saline media, polyampholytes carrying both positive charges and negative charges can be suitable. When the charges are in equal number (neutral polyampholytes) and the proton exchange is suppressed, the properties in aqueous solution of these products are governed by the attractive forces that exist between the unlike charges. They are generally more soluble and they have higher viscosities in a saline medium than in deionized water. The behaviour of this type of polymer is therefore referred to as antipolyelectrolyte behaviour.
In the case of polyampholytes that do not have the same number of positive and negative charges, according to the extent of the excess of one charge type in relation to the other, it is the polyelectrolyte effect or the neutral polyampholyte effect that characterizes the behaviour in solution (Corpart et al., Macromolecules, 1993, 26 (6), 1333).
These products are already mentioned for many applications, in particular for the formulation of cleaning compounds, cosmetic applications, the latter depending on the nature of the zwitterion, on their composition and on the molar mass of the polymer.
When the monomer comprises exactly an ammonium group and an anionic function, it belongs to the betaine family and the charges form an inner salt. A distinctive feature of the polymers of the invention is that the unlike charges are on the same side group of betaine type. These are electrically neutral polymers. The positive charge is provided by a quaternary ammonium function, the negative charge by a sulfonate (sulfobetaines) or phosphonate (phosphobetaines) group.
Some copolymers were obtained by copolymerization of acrylamide with carboxybetaine type monomers (Kathmann et al., Polymer, 1997, 38 (4), 871). Their properties in solution greatly depend on the pH value and they are incompatible with the desired properties. In fact, at a low pH value, the protonation of the carboxylate functions leads to the loss of the zwitterionic character and the copolymer behaves like a cationic polyelectrolyte, thus sensitive to the presence of salt in particular.
The polybetaines described here have the advantage of keeping their zwitterionic character within a wide pH range. Certain acrylaride and sulfobetaine copolymers have already been described, but they result from synthesis processes carried out in the presence of salts, which is of notable importance for the structures obtained.  less than  less than Hydrophilic sulphobetaine copolymers of acrylamide and 3-(2-acrylamido-2-methylpropanedimethylammonio)-1-propanesulphonate greater than  greater than  by L. Cormick et al.xe2x80x94POLYMER, 1992, Volume 33, Number 21.
The object of the invention relates to the synthesis and to the properties in solution of zwitterion copolymers. Zwitterionomer copolymers copolymerized with a more or less substituted acrylamide or acrylate correspond to the description of the general formula defined hereafter.
The general structure of the polymers is as follows: 
W is a CONH2 or CONHR or CONRRxe2x80x2 or COOxe2x88x92 or COORxe2x80x3 group, where R, Rxe2x80x2 and Rxe2x80x3 are linear or branched aliphatic radicals,
x, y, z are molar percentages, y+z not equal to zero,
D, E and F are an atom of hydrogen or a methyl group,
X and Xxe2x80x2 correspond to one of the following two formulas: 
R2 and R3 are each a monovalent hydrocarbon radical,
R1 is a divalent organic group comprising a linear chain consisting of carbon atoms, containing 3 to 12 atoms in linear chain, that can be interrupted by 1 nitrogen atom carrying an amide function or by 1 to 3 oxygen atoms and comprising possibly alkyl or hydroxyl substituents,
R4 is a linear or branched aliphatic group and R5 is a hydrocarbon radical,
Zxe2x88x92 meets at least one of the following formulas corresponding to sulfobetaines and phosphobetaines respectively: 
R9 is a methyl, phenyl or alkoxy radical,
in cases where synthesis of the polymers is carried out in the absence of salts:
(y+z) max=40%,
in the case of phosphobetaines and of synthesis in the presence of salts:
(y+z) max=100%.
In the case of sulfobetaines, R1 can be one of the following two formulas: 
wherein R6 and R7 represent each a substantially hydrocarbon radical and R8 a hydrogen atom or a hydrocarbon radical; n, m, p, q integers, n is 2 or 3; Y can be a methyl or hydroxyl group; p can be 0 or 1.
When Y is a hydroxyl group, p is 1, m is 1 and q is 1.
When Y is a methyl group, p is 1, m is 2 and q can be 0 or 1.
If p is 0, the sum m+q is 2, 3 or 4.
In the case of phosphobetaines, R1 can correspond to one of the following four formulas: 
r is an integer between 3 and 12, s is an integer between 1 and 3 and t is an integer that can be 1 or 2.
Synthesis of the Zwitterion Hydrosoluble Polymers
The general principle of the synthesis of the polymers of the invention, only limited by the term hydrosolubility, consists in polymerizing one or more monomers, at least one of them being zwitterionic, which goes into the composition of the initial copolymerization mixture. The polymer is obtained according to a known polymerization process in aqueous solution in the presence of a hydrosoluble radical polymerization initiator which can be potassium persulfate.
Synthesis of zwitterion monomers whose polar head nature (carboxylate, sulfonate, phosphonate), hydrocarbon skeleton structure, substituents nature, intercharge distances and polymerizable group nature can be adjusted by taking as the reference synthesis methods known from the prior art is intended to produce new zwitterion compounds, which are new in particular for their polymerizable nature (documents U.S. Pat. No. 4,704,229 and FR-2,572,078).
The operation of co- or ter-polymerization of two or more comonomers is then carried out by preparing comonomer mixtures placed in a reactor that is stirred and whose temperature is thermostat-controlled to allow completion of the copolymerization. The selected zwitterionomer compositions range between 0 and 100%, preferably between 0.1 and 40%, and in particular between 1 and 10%. The copolymerization temperature set at between 25 and 90xc2x0 C., preferably between 35 and 60xc2x0 C., is so determined as to obtain a copolymer after less than ten hours"" reaction and preferably between 1 and 3 hours"" reaction for conversion rates of the order of 10 to 80%, which are limited by the viscosity of the reaction medium.